U.S. Pat. No. 3,759,426 discloses a pump for mounting on a receptacle, the pump comprising a pushbutton that is movable relative to a pump body between a high position and a low position and that co-operates therewith to define a pump chamber of variable volume, the pump body having a vent suitable for communicating via a passage with the outside of the receptacle when the pushbutton is in an intermediate position between its high and low positions, thereby enabling air to enter into the receptacle while substance is being sucked into the pump chamber.
The pushbutton has an outer skirt suitable for isolating the vent when the pushbutton is in its high position and when it is in its low position. The pushbutton has an inner skirt which co-operates with the outer skirt to define a groove suitable for housing a return spring.
The outer skirt is exposed to the possibility of being dirtied, which dirt can then come into contact with the substance contained in the pump body.
In addition, the return spring is immersed in the substance, which can give rise to problems of compatibility.